This invention relates to tiltable chair arrangements and, more particularly it concerns a coil spring tilt mechanism disposed between a support base and the bottom of a chair.
Different forms of chair tilt mechanisms are known in the prior art. For example, tilt mechanisms incorporating a torsion bar arrangement to impart a return bias or torque to a chair have been proposed. Generally, these mechanisms have suffered from bulkiness and distracting operating characteristics. The bulkiness prevents the torsion bar mechanism from being readily adapted to the overall design of the chair thereby presenting a "mechanical" or clumsy appearance. Although torsion bar mechanisms do have linear or straight line performance characteristics, the ride given to the user of the chair may be hampered by a feel of friction and stickiness.
Tilt mechanisms employing a rubber pack-type resilient element are also known. These rubber packed mechanisms do overcome the feel of stickiness and friction from which torsion bar mechanisms have suffered. However, due to the non-linear characteristics of the rubber packed devices, a bouncy or "rubbery" feel is imparted to the user of the chair. This rubbery feel is usually more prevalent when the user of the chair is of a relatively low weight. With users having higher weights, the rubbery feeling due to the non-linear characteristics of the device decreases.
Various tilt mechanisms employing coil springs to impart the return torque have also been used. The coil springs, due to their straihgt line performance or linear characteristics generally provide a smoother and more comfortable ride when compared with tilt mechanisms employing either a torsion bar or a rubber pack. The feel of friction and stickiness is minimized or nearly eliminated.
However, coil spring devices have generally suffered from bulkiness and high weight. An exposed coil spring device is prone to the collection of dirt and dust, is very difficult to clean and is not easily adjustable to the needs of persons of different physical characteristics. Further, present coil spring tilt mechanisms do not have provision for the ready substitution of springs of different compression values.
Although coil springs may be preloaded to thereby require a greater initial force to be imparted to the chair by a user, due to the coil spring's linear characteristics, the incremental increase in force required to tilt the chair remains the same. As a result, one spring may provide an acceptable ride or degree of resistance to tilt for a person of relatively low weight while imparting to a person of relatively higher weight a feeling of looseness or instability. As a result, to completely tailor a chair to the individual user, the ability to substitute springs of different compression values is desirable.